Single 12 volt LiTime battery - charging issue

[stealthbob]

First off, this is not specifically about solar power, so I apologize. I just really like the vibes here and figured I could get the help I need.

I’m experiencing a sudden issue with my 12V 100Ah LiTime LiFePO4 battery. I use a charger set to 14.5V, typically charging at around 25A. This setup serves as a portable power bank for my camping trips. It has worked great for a year without any issues, but now a problem has arisen.

I suspect this may have happened because I attempted to charge it in cold conditions. The temperature was just above 0°C, but I assumed that would be safe, and I relied on the BMS to protect it (I’ve confirmed it has a low-temperature cut-off). Since then, when I charge at 14.5V, the battery reaches that voltage and holds it, indicating no current. Once I stop charging, the voltage quickly drops to around 13V within a couple of hours. Additionally, it seems like the BMS still has it locked out because when I try to charge again, the charger indicates 14.5V with no amps flowing. If I put a load on the battery for a while and then attempt to charge, it will take a charge, but only to end up with the same result.

Interestingly, if I charge at a lower voltage, around 14.2V, this issue does not occur. The battery reaches 14.2V and holds the charge normally. I assume this is due to the voltage not reaching the BMS cut out?

Could this simply be an imbalance? Is it possible I damaged a cell, and if so, is this irreversible? What’s the best way to balance a single battery? Most resources I’ve found focus on balancing multiple battery banks.

 

[Q-Dog]

It sounds like an imbalance. If you charge to 14.2 volts and the charger hits absorption for 15 - 30 minutes, you are fully charged.

 

[50ShadesOfDirt]

This is a LiFePO4 battery, so hopefully you are using a smart 12v battery charger with a "LiFePO4" charging profile ... if you have only a standard 12v battery charger (more for FLA or such), then that's one issue. Replace that charger asap with one designed to work with LiFePO4 batteries, of the right voltage. LiTime makes one, and many others have such chargers ...

Another check is to do a load test on the battery, and see where you are with aging/charging/capacity in general ... can you put power in, and get reasonable capacity (up to 100Ah) back out, or has something changed? An inexpensive load tester, bought or borrowed, helps determine if battery is still capabile of loads, regardless of voltage it shows ... over time and use, many batteries will still show "good" voltages, but just can't handle a load any longer.

I don't focus so much on voltages (to determine capacity), rather, I worry about how much capacity I can get out, before having to recharge. If I'm within 90 or 95%, I'm happy ... if I'm at 80 or 70, I start to dig deeper into what's going on, given that the battery manual says I should get several thousand cycles of 90% or more out of it before things drop off. Read your manual to find that set of numbers for your battery ...

Hope this helps ...

 

[mikefitz]

Could this simply be an imbalance

Yes. The BMS is detecting cell inbalance and shutting down the charge path, you are seeing this with the charge current going to zero. Once the battery is in protection you won't see true battery volts with a meter, common is a drop of around 0.5 volts, thus the 13 vo,ts you are seeing is an actual 13.5 volts internally, a fully charged battery.
There is no problem with the battery and the fact that is charges to 14.2 volts indicates that its charging successfully.
I doubt a cell is damaged, it probable that its not getting enough balance time.
If you can set your charger or power supply to hold the voltage at 14.2 for several hours after a full charge this should improve balance.
Just continue using the battery and charging to 14.2 as an alternative will still charge to full and overtime the balance will improve.

 

[stealthbob]

Thanks all...

So yea I am using a fully adjustable power supply for charging. In the past I used 14.5 volts and typically 25 amps. I did just charge to 14.5 last night and its now dropped to 12.85 and wont take a charge at any voltage. I will put a small load on it (light) and see if I can reset the BMS then just keep charging to 14.2 for a while as suggested.

Dang the support here is amazing!

Edit-so yea definitely a BMS cut off, I put a light on it and watched the voltage drift down to 12.8 and then bang up to 13.32. I then put the charger on it at 14.2 and 6 amps and it was taking it. As suggested I will leave it like this for a while....I assume it will help to keep a small load in it like a fan?

 

[Dagoth Ur Does Solar]

Thanks all...

So yea I am using a fully adjustable power supply for charging. In the past I used 14.5 volts and typically 25 amps. I did just charge to 14.5 last night and its now dropped to 12.85 and wont take a charge at any voltage. I will put a small load on it (light) and see if I can reset the BMS then just keep charging to 14.2 for a while as suggested.

Dang the support here is amazing!

Let us know what happens. When I got my LiTime 12V 230Ah, it capacity tested perfectly, but then I think at one point my had some drift because I wasn't giving it enough charge time to balance. I changed my setup to ensure it's getting enough charge time at ~100% and it seems to be back to normal, everything has been fine since then.

These LiFePO4 batteries definitely have to be charged to 100% pretty regularly to make sure they're staying balanced. I think most of these BMSes from the factories are set to only balance while charging.

 

[stealthbob]

Ok so some strange behavior observed...

So after removing from the 14.2 charge I put a small load using a bed side light and the voltage dropped as predictive. It did however jump back up to 13.8 to only start dropping again...going past 13.32. I put two fans on as a load to start discharging but after a while the voltage jumped back up to 13.32 and is holding there for the last hour at 13.32 (+/- 0.05).

Is this a sign of balancing? ...are the higher voltage cells coming down? This tech is so foreign to my understanding of expected battery behavior.

 

[TacomaJoe]

I think part of what you're seeing is a quirk of the LiTime BMS. If you have a constant load on the battery, the voltage shouldn't jump around any. The voltage during discharge will drop from the 14.2V into the ~13.7V range for the duration until you get to the lower knee.

If you remove the load the BMS may turn off the FETS and give a jump in voltage reading with a high impedance meter.

Cell balance only shows up at the top and bottom of the charge. In the 13.7V flat range, you couldn't really detect any imbalance. At the top a cell imbalance will put one cell hitting say 3.6V and the BMS cuts off the charging while the other cells are still on the way up so they don't get fully charged. During charge and discharge the cell voltage changes slowly, no sudden jumps no matter how imbalanced they are.

 

[mikefitz]

put a small load using a bed side light

It needs a load of a few amps to recover fully from charge protection. Once the volts drop below cell overvolt recovery level, the battery will behave correctly. Cell balancing will only occur, a) when any cell is greater than 'start balance voltage', typically 3.4 to 3.5 volts, and b) for many BMS, when there is charge current. The passive balancing used in low cost batteries only 'bleeds ' a small current from the 'high' cell, thus even for a low degree of inbalance, it can take some time for the cells to balance to a similar voltages at a battery high SOC.

 

[stealthbob]

Okay, I think I can close this issue now...it seems to have recovered. I really appreciate all the info; it was helpful to get multiple replies since I could take little tidbits from each post to build a clearer picture. Also, this guy was pretty helpful: YouTube link.

I ended up charging at 14.2 volts and 500mA for 24 hours. After removing the charger, the voltage stabilized at 13.33V and has remained steady for a while. I get the feeling this battery was never properly balanced and came like this from the factory.

I also decided to order a nice bench power supply with graphing capabilities...something I've been wanting for years to support other projects, so it was finally time. Once it arrives, my next step will be to charge at 14.5V and 150mA and see if the BMS cuts off before reaching that level. This will allow me to determine the exact cutoff point. If it shuts off at 14.5V, great. If not, I can redo the test at just below the cutoff voltage and hold it there for another 24 hours.

Regarding the top voltage, I assume 14.5V is a conservative limit that doesn’t sacrifice much capacity. However, if the pack is healthy, I should be able to take it up to 14.6V, right? Or would it be better to leave some margin and stick with 14.5V? If I’m misunderstanding anything, please let me know.

 

[Q-Dog]

At 14.2 volts absorption you are fully charged. No need to go any higher.

 

[Sabre36]

The recommended charge rate is 20A. /.2C

 

[stealthbob]

The recommended charge rate is 20A. /.2C

Yea, I was playing with low charge rates to make it easier to catch the BMS cut off voltage. 20A has always been my goto charge rate, I use a small suitcase style 1000w generator when in the field so I also dont like stressing that too much as well.

 

[stealthbob]

At 14.2 volts absorption you are fully charged. No need to go any higher.

Ok so I tried sneaking up on the 14.2 charging at 150mA just to see exactly where the BMS cuts it off, it stopped at 13.9. So would this mean I have to use 13.8 and hold it there to get the passive balance to work? This is the last time I get a LiFePo battery without BT displaying individual voltages for each cell. Hell I think I will just build my next one myself so I can maintain it better.

 

[mikefitz]

would this mean I have to use 13.8 and hold it there to get the passive balance to work?

Yes, after several hours you should see some improvement.

 

[Q-Dog]

Just use it. Draw it down by about 25ah and charge it back up ... do this a few times and see if it improves. Some manufacturers recommend you discharge/recharge, 100% - 0% - 100%, to balance the battery. I don't think you need to go that deep, but it can't hurt if you have the time.

 

[stealthbob]

Just use it. Draw it down by about 25ah and charge it back up ... do this a few times and see if it improves. Some manufacturers recommend you discharge/recharge, 100% - 0% - 100%, to balance the battery. I don't think you need to go that deep, but it can't hurt if you have the time.

Yeah, I don’t mind taking action myself to help improve this, and I’ll continue trying. I just want to know the best way to improve it rather than guessing. I’ll do some more full cycles as you mentioned.

I’ve also engaged with a LiTime rep in their Facebook group. I followed their instructions and posted the results, which I believe demonstrated that there is an issue. However, at some point, I’ll give up on all this. The time and energy I’m putting in are starting to exceed the value of the desired result.

 

[Q-Dog]

Does the battery give full capacity?

 

[stealthbob]

Does the battery give full capacity?

Can you suggest a good way to measure that, I assume a known load and then time it...is it that simple?

 

[Q-Dog]

Can you suggest a good way to measure that, I assume a known load and then time it...is it that simple?

Yes. Or a good shunt/battery monitor.

I'm curious why you worry about cell balance when you have no idea what the actual capacity is? I've said a couple of times now it sounds like your battery is fully charged.

 

[stealthbob]

Yes. Or a good shunt/battery monitor.

I'm curious why you worry about cell balance when you have no idea what the actual capacity is? I've said a couple of times now it sounds like your battery is fully charged.

Ok, perhaps my understanding is off...is it possible to get full capacity when I can only charge to 13.9 volts? If so I appreciate you changing my understanding, all my info has come from YouTube University so yea....I might be a little off.

 

[Q-Dog]

is it possible to get full capacity when I can only charge to 13.9 volts?

Yes, if you hold it there long enough.

 

[outboard1196]

Ok, perhaps my understanding is off...is it possible to get full capacity when I can only charge to 13.9 volts? If so I appreciate you changing my understanding, all my info has come from YouTube University so yea....I might be a little off.

You should be able to charge to 14.2 without issue.
I'd try holding 13.8 for a few hours and try sneaking up on 14.1 by .1v increments.
I did have a weird issue with litime as well, when the battery was sitting idle the voltage rose with nothing but the smart shunt attacched. I made a post about it.

Thread 'Weird voltage rise.'

Nov 22, 2024

I have a litime 12v battery, had an issue getting it balanced out of the box. Floated it at 13.8v then charged and seemed to complete charging fine over night.
This morning I unplugged the victron wall charger ( left the leads hooked to the battery)
Just now I went to loom at the smart shunt data to see how it looked at the end of charge and noticed a weird voltage rise not too long ago. Went from 13.23 to 13.76v I did remove the charger leads tonight but not sure the time.
I hooked the charger leads back up but the voltage didn't change. I have a small inverter hooked up but hasn't been...

• outboard1196
• Replies: 12
• Forum: Beginner Friendly "Plug-n-Play" Lithium Batteries